1. Field of the Invention
The present invention relates to ink compositions and an ink set comprising the same that can be preferably used in ink jet recording.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto a recording medium such as paper to conduct printing. This method has a feature that an image having high resolution and quality can be printed at a high speed by means of a relatively inexpensive apparatus.
In general, the ink composition used in the ink jet recording comprises water as a main component and, added thereto, a colorant and a wetting agent, such as glycerin, for preventing clogging and other purposes. Water-soluble dyes, by virtue of high chroma of the colorant, abundance in types of usable colorants, solubility in water and other advantageous properties, have been extensively used as the colorant in the ink composition for ink jet recording.
The dyes are, however, generally poor in lightfastness, waterfastness and other various properties. Therefore, prints obtained using dye ink compositions have poor lightfastness and wasterfastness. The waterfastness has been improved through the use of specialty recording papers having an ink absorptive layer for ink jet recording. For plain papers, however, the improvement in waterfastness is still unsatisfactory.
Pigments, as compared with the dyes, have superior lightfastness and waterfastness. This has recently led to studies on utilization of pigments as colorants in the ink composition for ink jet recording from the viewpoint of improving the lightfastness and waterfastness of printed images. Pigments are generally insoluble in water. Thus, when a pigment is used in a water-based ink composition, a method should be used which comprises mixing the pigment with a resin called a xe2x80x9cdispersantxe2x80x9d to prepare a mixture, stably dispersing the mixture in water, and then preparing an ink composition using the dispersion.
In order to stably disperse pigments in a water system, studies should be made on the kind and particle diameter of pigment, the kind of resin used, dispersing means and the like. Up to now, a large number of dispersing methods and inks for ink jet recording have been proposed in the art. For example, Japanese Patent Laid-Open No. 252467/1991 proposes an ink composition comprising water, a styrene/maleic acid copolymer, xcex5-caprolactam, and a pigment, and Japanese Patent Laid-Open No. 79680/1991 proposes an ink composition comprising an aqueous medium, a styrene/maleic acid copolymer, and a copper phthalocyanine pigment.
Further, for ink compositions comprising pigments as the colorant, a task to be accomplished is to improve the rubbing/scratch resistance of printed images. Unlike dyes penetrable into recording media, pigments stay on the surface of recording media, making it necessary to improve the rubbing/scratch resistance using some means.
When utilization of pigments as the colorant for inks for ink jet recording is considered, as compared with dyes, pigments have superior lightfastness and waterfastness, but on the other hand are smaller in number of kinds of usable colorants. In practical use of inks for ink jet recording, hue besides lightfastness and waterfastness should be sufficiently studied.
Furthermore, a proposal has been made for enhancing the penetration of the ink composition, shortening the drying time, and forming a large pixel (for example, a dot) using a smaller amount of the ink used. In pigment-based ink compositions, however, no satisfactory penetration is often provided due to the relation with the pigments and other ingredients.
On the other hand, regarding the ink jet recording method, the application of a polyvalent metal salt solution onto a recording medium followed by the application of an ink composition containing a dye having at least one carboxyl group has been recently proposed (for example, Japanese Patent Laid-Open No. 202328/1993). The claimed advantage of this method is that the polyvalent metal ion combines with the dye to form an insoluble complex, the presence of which can offer an image having waterfastness and high quality free from color bleeding.
Further, the use of a color ink comprising at least a surfactant for imparting a penetrating property or a solvent having a penetrating property and a salt in combination with a black ink capable of being thickened or agglomerated through the action of the salt has been proposed in the art (Japanese Patent Laid-Open No. 106735/1994). The claimed advantage of this method is that high-quality color images having high image density and free from color bleeding can be yielded. Specifically, an ink jet recording method has been proposed wherein two liquids, a first liquid containing a salt and a second liquid of an ink composition, are printed to realize good images.
In recent years, formation of color images by ink jet recording using a plurality of color ink compositions has been performed in the art. Color images are generally performed using three colors of a yellow ink composition, a magenta ink composition, and a cyan ink composition, and, in some cases, four colors of the above three color compositions plus a black ink composition. What is required of ink compositions for the formation of such color images is that they as such can exhibit good color development and, in addition, when used in combination with a plurality of ink compositions, can develop good intermediate colors.
The present inventors have now found that an ink composition comprising a specific pigment in combination with specific other ingredients can realize an image possessing excellent rubbing/scratch resistance and color reproduction in color ink jet recording and has advantages as a superpenetrating ink composition. The present invention has been made based on such finding.
It is an object of the present invention to provide as the first aspect of the present invention cyan, magenta, yellow, and black ink compositions and orange and green ink compositions that have good lightfastness and waterfastness and at the same time can realize good images, especially images having good hue.
The cyan, magenta, yellow, and black ink compositions according to one aspect of the present invention are an ink composition comprising at least a colorant, water, a water-soluble dispersant, and a penetrant, the colorant comprising 2 to 4% by weight of C.I. Pigment Blue 15:3, 3 to 5% by weight of C.I. Pigment Red 122, 3 to 5% by weight of C.I. Pigment Yellow 74 or 128, 2 to 5% by weight of carbon black, and C.I. Pigment Orange 43 or 36, or C.I. Pigment Green 7 or 36, the penetrant being 0.1 to 5% by weight of an acetylene glycol compound, the water-soluble dispersant being a water-soluble styrene/(meth)acrylic acid resin in an amount of 0.1 to 1 part by weight on a solid basis based on the pigment.
The ink composition of the present invention can realize images having excellent rubbing/scratch resistance and color reproduction. In color printing using ink compositions, in general, a yellow ink composition, a magenta ink composition, a cyan ink composition, and optionally a black ink composition are used with controlled amount of deposition to reproduce colors. Color reproduction is influenced by the kind of the pigment, the concentration of the pigment, and the kind, amount and the like of ingredients of the ink composition other than the colorant, for example, a dispersant. In color printing, especially ink jet recording, using the conventional pigment-based ink composition, the color reproduction is inferior to that in the case of dye-based ink compositions and hence has been required to be improved for practical use. By contrast, the ink composition of the present invention can offer color reproduction equal to the dye-based ink composition despite the fact that the pigment is used as the colorant. Further, the ink composition of the present invention has advantages as a superpenetrating ink composition. Specifically, the drying time is short, and a large pixel (dot) can be formed in a smaller amount of the ink used.
The present inventors have further found that use of an orange ink composition and/or a green ink composition in combination with a yellow ink composition, a magenta ink composition, and a cyan ink composition, which have hitherto been used in color ink jet recording, can provide better color images. They have also found that a combination of color ink compositions using specific pigments can realize better color images. The present invention has been made based on such finding.
Accordingly, it is another object of the present invention to provide as the second aspect of the present invention a color ink set that can realize good color images, especially images having good hue in ink jet recording.
The ink set for ink jet recording according to the second aspect of the present invention consists essentially of three ink compositions, a yellow ink composition, a magenta ink composition, and a cyan ink composition, and, in addition, an orange ink composition and/or a green ink composition.